i always like k&n intakes.....ive never messed with anything else until i made my own, then i recently threw my $30.00 iceman on my car and that seems to do the best so far....however i dont use anything but k&n filters...being that they seem to hold up the best, ive ran one over(and still use it), another was on my car when my inner cv joint/boot went out and coverd half of it with grease(cleaned it and still works good)....they just seem to be alot more durable

 

its good you brought up filters. those cheap intakes on ebay dont always come with the best filters. if you get say K&N, your getting a good quality filter. airflow has as much to do with an effective filter (that blocks bad and lets through good) as it does with the bends and twists the air must go through.
cheap welds will break easier, the cheaper ones may skimp on welding and quality of 'bending' the metal. but i have heard numerous people who are quite happy with the $30 ones. but i have heard of welds breaking and less than perfect fits, not so much with ram-air but with cold air where it actually goes into the fender.

if your putting on an intake, there is really no need for an exhaust upgrade uless you want to. if you have other mods it may behoove you to put a larger exhaust. also, if you plan on going all-out on your motor get a full 3" intake. otherwise its not really necessary.

 

oh and, metal intakes have more of a pinging sound in the high rpm ranges and plastic have a low growl.....i like the plastic the most

 

the material can make a little difference as far as transfering heat to the incoming air, however this gain is rahter minimal (especially when using a ram intake). but your right about the sound, especially the 'rattle' or flutter you hear when the turbo blades are spinning and you let off the throttle.